The present invention relates to an ice making machine, and more particularly to a cube ice making machine utilizing a defrost harvest cycle with assisted ice release.
There are several major types of automatic ice making machines. Predominant forms of ice produced in such machines are cubes and flakes. Cubes are preferred for cooling carbonated beverages served in cups because cube ice generally causes less foaming of the beverage.
Cube ice making machines themselves come in a number of varieties. Some form individual ice cubes, while others, referred to as slab-type machines, have a grid of ice forming pockets that freeze individual cubes. When the cubes are to be harvested, the ice starts to melt. Just as water expands as it freezes into ice, the ice and water contract as the ice starts to melt. This creates a vacuum in the pockets. In addition, as the ice tries to slide out of the pockets, the surface tension of the water holds the water between the ice cube and the grid side walls. This adds to the vacuum, which must be broken before the cubes will slide out of the pockets. Preferably, ice is allowed to freeze over the edges of the grid to bridge between individual cubes. When it is time to harvest the cubes, the ice bridge holds the cubes together and makes the cubes all come out in one slab once the vacuum is overcome, thus helping to achieve a complete harvest.
The thickness of the bridge can be controlled by adjusting an ice thickness sensor. Usually a thicker bridge is desirable from a harvest standpoint, so that all of the cubes come out with the slab. Also, it has been found that larger ice bridges cause the ice to harvest in a shorter amount of time. On the other hand, thick ice bridges prevent the individual cubes from breaking apart when the ice falls into a bin. Large clumps must be broken up with a scoop before the ice can be added to a cup. Also, because the ice acts as an insulator, it takes longer to form the next incremental layer of ice the thicker the ice bridge becomes. In terms of the overall production rate of the machine, this offsets the benefit of faster harvest times achieved with thicker ice bridges.
Many cube ice machines use a xe2x80x9chot gas defrost systemxe2x80x9d to heat the ice-forming mold to harvest the ice. In these machines, hot refrigerant vapor from the compressor is routed through a hot gas valve to bypass the condenser and expansion device in the normal refrigeration system. The hot refrigerant is fed directly into the evaporator. During the harvest cycle, the evaporator actually works as a condenser. The refrigerant cools and condenses, and the latent heat of the phase change of the refrigerant is used to xe2x80x9cdefrostxe2x80x9d the evaporator and heat the ice-forming mold. This system is very reliable, but has a number of drawbacks. First, condensed refrigerant may be returned to the compressor. Compressors can be damaged if too much refrigerant is condensed and returned in a liquid state. Also, the heat added to the evaporator melts ice that was previously frozen, reducing the ice production for that cycle. Also, heat that increases the temperature of the ice-forming mold must be removed in the next freeze cycle. Thus the hot gas defrost cycle has a negative impact on the energy efficiency of the ice machine, measured in terms of pounds of ice produced per kilowatt-hour (kwh) of electricity used.
In many refrigeration systems, such as home air conditioners, energy efficiency can be improved by reducing the size of the compressor and using a lower head pressure, and utilizing a larger evaporator. However, in an ice machine using hot gas defrost, this approach would have only a limited improvement on efficiency, because the smaller compressor and larger evaporator would cause a longer defrost cycle. The machine would thus spend more of its time in the harvest mode. The amount of ice produced in a given quantity of time would then be reduced. Thus, even though less energy is required to operate the machine, less ice is produced during the time it is running.
U.S. Pat. No. 4,341,087 and No. 4,366,679 disclose an ice making machine with a mechanical device to assist the harvest. A harvesting plunger is activated by a motor to push through the back side of an evaporator plate against one of the cubes of ice in the ice-forming mold. In theory this plunger thus acts to push the entire slab of ice out of the ice-forming mold in a reduced harvest time. The reduced harvest time results in greater theoretical efficiency. However, in practice, commercial ice making machines with this mechanical harvest assist have had reliability problems. Sometimes only the cube of ice being pushed against by the harvesting plunger, and perhaps a few surrounding cubes, are ejected. Since the remaining ice is not pushed out, the machine goes back into a freeze cycle without harvesting all of the ice.
Another commercial ice making machine uses water to wash down over the front of ice cubes that are formed in individual pockets during a harvest cycle. While this speeds up the harvest cycle, it also produces xe2x80x9cwet icexe2x80x9d. When wet ice sits in an ice storage bin, the ice cubes tend to freeze together.
Another commercial ice making machine uses water on the back side of the ice-forming mold to help quickly defrost and harvest the ice. However, this approach has its own drawbacks. The water used to defrost is then used as make-up water for the next batch of ice. The back side of the ice-forming mold is not very accessible or cleanable. Therefore using the water that has flowed over the back side of the ice-forming mold to make ice which will be consumed is a very questionable practice from a sanitation standpoint.
U.S. Pat. No. 4,489,567 discloses an ice machine that also uses a mechanical pusher to help assist in ice harvest. However, the pusher is spring activated. A diaphragm with water pressure holds the spring and plunger back during the freeze cycle. This design has never been commercially practiced, in part because of the same reliability problems encountered with the motor driven pusher in U.S. Pat. No. 4,341,087.
U.S. Pat. No. 4,843,827 discloses an apparatus for making ice cubes that vibrates the ice forming mold to help release the ice cubes during harvest. The ice forming mold is made with breather vents in the back side of each ice-forming pocket. The patent goes on to state that positive pressure could be introduced through these breather vents. While no source for the positive pressure is shown, a simple diaphragm compressor is suggested. To the best of applicants"" knowledge, no commercial equipment has been made following the teachings of this patent. Further, it appears that the design of the ice-forming mold is for making only individual cubes, and not slab ice. Also, the air vents are all connected together. Thus, once one of the cubes of ice is released, the air pressure in the entire system would be relieved through the vent hole where the ice cube is no longer blocking it, and no pressure would build up to help push other ice cubes out.
It would be very beneficial if a reliable method were developed that would improve the energy efficiency of ice making machines. A method that would shorten the duration of the harvest cycle without encountering the problems of sanitation, reliability, wet ice or commercial non-viability would also be a significant benefit.
A method of making and harvesting ice cubes in a more energy efficient manner, without the drawbacks enumerated above, and an ice-making machine for practicing the method, have now been invented.
In a first aspect, the present invention is an ice making machine comprising a refrigeration system including a compressor, a condenser, an expansion device, an evaporator made with refrigerant channels formed in a serpentine shape, and interconnecting lines therefore; a water system including a pump and an ice-forming mold having a back surface and an open front face to form a slab of ice, the serpentine channels of the evaporator being in thermal contact with the back surface of the ice-forming mold; and interconnecting lines therefore; and a harvest assist system comprising the at least one hole through the back surface of the ice-forming mold and a source of pressurized fluid, either liquid or gas, connected to the at least one hole.
In a second aspect the present invention is a method of making and harvesting ice cubes comprising freezing water in an ice-forming mold having a back surface, an open front face and dividers mounted on the back surface forming pockets for the formation of individual ice cubes, the water also forming ice bridges between the ice formed in the pockets, thus forming a slab of ice cubes; heating the ice-forming mold to release the ice cubes from their individual pockets; and using pressurized fluid to break the vacuum and begin to push the frozen slab of ice cubes out of the ice-forming mold.
In a third aspect, the present invention is a method of improving the energy efficiency of an ice making machine that forms individual cubes of ice in an ice-forming mold with ice bridges between the cubes to form a slab, the improvement comprising introducing pressurized air between the slab of ice and the ice-forming mold in conjunction with heating the ice-forming mold to assist release of the cubes of ice.
The preferred ice making machine uses pressurized air, introduced at strategic locations, behind the slab of ice to dramatically shorten the harvest cycle time. Because the harvest cycle is shorter, less heat energy is put back into the ice-forming mold. Thus, not only is more of the compressor run time used to freeze ice, but the heat needed to be removed by the refrigeration system at the end of the harvest cycle to cool the ice-forming mold back to a freezing temperature is reduced. The system is also proving to be highly reliable, with an evenly applied force to prevent one cube from being popped out of the slab, leaving the rest behind. Unexpectedly, the best efficiencies in harvest time have been found to coincide with a fairly thin ice bridge. This results in cubes which easily separate from one another when they fall into an ice bin, giving customers desirable independent ice cubes at the same time as high energy efficiency.
The invention is also useful with ice machines that use other types of defrost systems. U.S. Pat. No. 6,196,007, which is hereby incorporated by reference, discloses a cube ice making machine that uses cool refrigerant vapor to defrost the evaporator and harvest the ice. The present invention can improve the harvest time on such a cool vapor defrost system. As can be seen in this patent, it is not necessary for all parts of the ice machine to be housed in the same cabinet
These and other advantages of the invention, as well as the invention itself, will be best understood in light of the attached drawings.